How to Undelete Files on XFS Filesystem

There are a couple different options for undeleting files for XFS filesystems.

TestDisk

TestDisk is a great command line recovery tool. Unfortunately, it can be slightly more difficult on systems using XFS compared to EXT4 systems. TestDisk does not support undeleting a file in place on XFS.

You can still recover files using TestDisk, you just need to recover the whole drive and dig through the recovery results to find the files you want.

xfs_undelete

There is also another utility that can be helpful. xfs_undelete

https://github.com/ianka/xfs_undelete

It allows for a little more flexibility in recovering files. For instance, you can specify to recover the files from the past hour to recover.

Download prerequisites

sudo dnf install tcllib
wget https://raw.githubusercontent.com/ianka/xfs_undelete/master/xfs_undelete
chmod u+x ./xfs_undelete

./xfs_undelete

Example of running xfs_undelete

./xfs_undelete -t -1hour ./dev/sda2

You will need a different filesystem to save the files to. Otherwise you will receive the following error.

Your output directory is  /home/bob/recovery/
That is within the filesystem  /  you want to recover files
from. This isn't feasible as it would overwrite the deleted files you wanted to
recover. Please specify the option -o /path/to/output_directory on another (rw
mounted) filesystem or run xfs_undelete from within a directory on that
filesystem so the recovered files could be written there. They cannot be
recovered in place.

It’s not the greatest idea to recover on the system while running. Ideally, shut the system down, plug the drive into another machine as read only, and copy the files off.

You could also boot up in single user mode or a live Linux iso/thumbdrive and mount another recovery drive. Should work for both physical and virtual environments.

Enable Syslog for PowerDNS Recursor

  1. Enable Logging in PowerDNS Recursor Config
  2. Edit Systemd Unit File for PowerDNS to Allow Syslog
  3. Enable Logging in rsyslog Config File

The following links were helpful in setting things up.

https://doc.powerdns.com/recursor/running.html
https://www.reddit.com/r/linuxadmin/comments/9lc4jl/logging_queries_in_pdnsrecursor/

Enable logging in PowerDNS Recursor Config

First we need to find the line that says “disable-syslog” and uncomment/change it to

disable-syslog=no

Next find the line that says “quiet” and uncomment/change it to

quiet=no

Some other lines you may want to check and change

logging-facality=1
loglevel=6

Edit Systemd Unit File for PowerDNS to allow Syslog

Next we need to modify the Systemd unit file to allow PowerDNS Recursor to log to syslog.

systemctl edit --full pdns-recursor.service

On the ExecStart Line, remove the part that says

--disable-syslog

The resulting line should look something like

[Service]
ExecStart=/usr/sbin/pdns_recursor --socket-dir=%t/pdns-recursor --socket-dir=%t/pdns-recursor --daemon=no --write-pid=no --log-timestamp=no

Save the file.

Enable Logging in rsyslog Config File

Edit the rsyslog file

sudo vim /etc/rsyslog.conf

Add the following line

local1.*        /var/log/pdns_recursor.log

This should now log all of the PowerDNS Recursor log info to “/var/log/pdns_recursor.log”

Restart the rsyslog and PowerDNS Recursor service

sudo systemctl restart rsyslog
sudo systemctl restart pdns-recursor

You should now see DNS request in the log file.

tail /var/log/pdns_recursor.log

They should also show up in the “/var/log/messages”

Cannot load Zend OPcache – it was already loaded

Started getting the following error while running ./validate.php for LibreNMS

Cannot load Zend OPcache - it was already loaded

Looks like the problem arises out of PHP trying to load two ini files for OPcache. Was trying to enable OPcache for LibreNMS so I created an opcache.ini file and put the settings in it. I missed the default 10-opcache.ini file.

Moving all the settings into the 10-opcache.ini file and deleting the created opcache.ini file resolved the issue for me.

https://unix.stackexchange.com/questions/253448/php-7-install-throws-cannot-load-zend-opcache-it-was-already-loaded-error/253484

How To Reset root Password on CentOS VM – XenServer

Basic steps are as follows.

  1. Shutdown VM
  2. From XenCenter, insert the CentOS iso into the VM’s Virtual DVD drive.
  3. Boot the CentOS VM in recovery mode.  If you need help with that check this post out.
  4. On the grub menu, select recover OS Installation.
  5. Run through the recovery and mount the VM’s disk where CentOS is installed
  6. You should now be able to drop to a prompt and chroot /sysimage
  7. Change the root password with passwd
  8. Shutdown the VM
  9. Eject the CentOS iso
  10. Boot up the VM and login with the new password

Install Ruby 2.6.1 via RVM on CentOS

Install Prerequisites

yum install -y curl gcc-c++ patch readline readline-devel zlib zlib-devel libyaml-devel libffi-devel openssl-devel make cmake bzip2 autoconf automake libtool bison libssh2-devel libicu-devel

Install RVM

curl -L get.rvm.io | bash -s stable

Setup RVM, install Ruby 2.6.1 and set to default.

source /etc/profile.d/rvm.sh 
rvm install 2.6.1
rvm use --default 2.6.1

You may need to add root or the user your using to the rvm group

sudo usermod -G rvm username

Pulled some of the info from here https://github.com/ytti/oxidized#installing-ruby-212-using-rvm

LibreNMS enable RRDCached on CentOS 7

Commands from https://docs.librenms.org/Extensions/RRDCached/

Create System Service

sudo vi /etc/systemd/system/rrdcached.service
[Unit]
Description=Data caching daemon for rrdtool
After=network.service
[Service]
Type=forking
PIDFile=/run/rrdcached.pid
ExecStart=/usr/bin/rrdcached -w 1800 -z 1800 -f 3600 -s librenms -U librenms -G librenms -B -R -j /var/tmp -l unix:/run/rrdcached.sock -t 4 -F -b /opt/librenms/rrd/
[Install]
WantedBy=default.target

Save with esc + :wq

Enable rrdcached service on boot up and start the service now

systemctl enable --now rrdcached.service

Enable RRDcached in librenms config

vi /opt/librenms/config.php

add/edit the following line. If it is commented out, uncomment it

$config['rrdcached'] = "unix:/run/rrdcached.sock";

Save with esc + :wq

Check the disk IO after a little bit to see if it went down.